JP6458759B2 - Stress relaxation structure and thermoelectric conversion module - Google Patents

Description

  The present invention relates to a stress relaxation structure and a thermoelectric conversion module.

  Conventionally, a thermal conductive stress relaxation structure excellent in thermal conductivity and thermal stress relaxation from a high temperature body to a low temperature body is known (see Patent Document 1 below). Patent Document 1 describes the necessity of efficient heat conduction for stably operating a device or instrument that generates heat, reduction of thermal stress for achieving high durability or high reliability of the device or instrument, or In view of the importance of relaxation, a structure that is relatively easy to manufacture and that can achieve both thermal conductivity and thermal stress relaxation is disclosed.

  Further, an invention relating to a joined body, a semiconductor device using the same, and a method for manufacturing the same is known (see Patent Document 2 below). In Patent Document 2, the connection member formed by solder printing and reflow has a problem that the array cannot be densely arranged, and the electrical resistance and thermal resistance increase, and stress can be relieved. And a joined body capable of reducing thermal resistance.

JP, 2014-143400, A JP 2014-183256 A

  For example, in a thermoelectric conversion module used for energy recovery from waste heat and a semiconductor device used for an inverter or the like, a thermal cycle in which a high temperature state and a low temperature state are repeated over a long period of time occurs. In order to stably operate equipment and devices that are exposed to such a heat cycle, it is necessary to improve the heat transfer efficiency from the high temperature side to the low temperature side. In addition, thermal stress due to the difference in thermal expansion coefficient is generated in each member constituting the apparatus and equipment. Therefore, in order to ensure long-term reliability, it is important to relax thermal stress between the respective members.

  As a stress relaxation structure for that purpose, a structure in which a thermally conductive ribbon or sheet is wound is conventionally used. This is because by using the stress relaxation structure of this structure, the effect of absorbing the strain generated between the members and relaxing the thermal stress can be obtained.

  For example, the thermally conductive stress relaxation structure described in Patent Document 1 is composed of an assembly in which thermal conductive materials are assembled in a non-bonded state, and the assembly includes, for example, a carbon-based sheet material and a metal-based sheet material alternately. (For example, refer to the claims). This structure has both thermal conductivity and thermal stress relaxation by using a carbon-based sheet material and a metal-based sheet material for the wound body. However, the carbon-based sheet material is inferior in bondability with a member to be bonded to the structure, which may reduce the bonding reliability of the structure and decrease the vibration resistance.

  Further, the semiconductor device described in Patent Document 2 includes a winding part and a stress relaxation part as a joined body that joins the first member and the second member so as to be capable of energization and heat transfer. A strip-like foil-like material having high electrical conductivity and heat conductivity such as aluminum is wound up (see, for example, claim 1, paragraphs 0012 to 0017). However, when the wound part is made of only a normal metal foil, the thermal stress relaxation property of the joined body may be lowered.

  The present invention has been made in view of the above problems, and includes a stress relaxation structure that can achieve both thermal conductivity and thermal stress relaxation and has excellent vibration resistance, and the stress relaxation structure. An object is to provide a thermoelectric conversion module.

  In order to achieve the above object, the stress relaxation structure of the present invention is a stress relaxation structure including a wound body in which a first thermal conductor and a second thermal conductor are alternately wound, The first heat conductor is a metal foil, and the second heat conductor is a porous metal foil.

  ADVANTAGE OF THE INVENTION According to this invention, thermal conductivity and thermal stress relaxation property can be made compatible, and the thermoelectric conversion module provided with the stress relaxation structure body which was excellent in vibration resistance, and the stress relaxation structure body can be provided. .

The typical perspective view of the stress relaxation structure concerning the embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a stress relaxation structure along the line II-II shown in FIG. 1. The schematic diagram explaining an example of the manufacturing method of the stress relaxation structure shown in FIG. The schematic diagram explaining an example of the manufacturing method of the stress relaxation structure shown in FIG. The typical sectional view of the thermoelectric conversion module concerning the embodiment of the present invention. Typical sectional drawing explaining the manufacturing method of the thermoelectric conversion module shown in FIG. Typical sectional drawing explaining the manufacturing method of the thermoelectric conversion module shown in FIG. Typical sectional drawing explaining the manufacturing method of the thermoelectric conversion module shown in FIG. Typical sectional drawing explaining the manufacturing method of the thermoelectric conversion module shown in FIG. Typical sectional drawing explaining the manufacturing method of the thermoelectric conversion module shown in FIG. Typical sectional drawing explaining the manufacturing method of the thermoelectric conversion module shown in FIG. FIG. 2 is a schematic cross-sectional view of an insulating substrate using the stress relaxation structure shown in FIG. 1. The graph which shows the relationship of the initial joining strength of the stress relaxation structure of an Example and a comparative example.

  Hereinafter, embodiments of the stress relaxation structure of the present invention will be described in detail with reference to the drawings.

[Stress relaxation structure]
FIG. 1 is a schematic perspective view of a stress relaxation structure 10 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the stress relaxation structure 10 taken along the line II-II shown in FIG.

  The stress relaxation structure 10 of the present embodiment includes a wound body 3 in which the first thermal conductor 1 and the second thermal conductor 2 are alternately wound. The first heat conductor 1 is a metal foil, and the second heat conductor 2 is a porous metal foil. In addition, as the stress relaxation structure 10, a structure in which the first thermal conductor 1 and the second thermal conductor 2 constituting the wound body 3 are joined can be used.

  Although the material of the metal foil of the 1st heat conductor 1 and the porous metal foil of the 2nd heat conductor 2 will not be specifically limited if it is a metal excellent in heat conductivity, For example, using copper or nickel Preferably, it is copper having higher thermal conductivity. The metal foil of the first heat conductor 1 and the porous metal foil of the second heat conductor 2 may be made of one material or a combination of two or more materials having different materials or characteristics. It is preferable that it is a continuous body like a belt.

  As the porous metal foil of the second heat conductor 2, for example, a porous film by electroless copper plating described in Journal of Japan Institute of Electronics Packaging, Vol. 1 (1998), No. 1, P66-69 is used. be able to.

  In the stress relaxation structure 10 of this embodiment, the wound body 3 includes a core material 4 at the center. The first heat conductor 1 and the second heat conductor 2 are alternately wound around the core material 4. In the example shown in FIGS. 1 and 2, the core material 4 has a cylindrical shape, but the shape of the core material 4 is not limited to the cylindrical shape. The core material 4 may have a cylindrical shape such as a plate shape, a polygonal column shape, or a cylindrical shape, for example. The material of the core material 4 is not particularly limited as long as the material has good thermal conductivity and heat resistance. For example, a metal material or an inorganic material can be used. Since the stress relaxation structure 10 includes the core member 4, there is an effect that the first thermal conductor 1 and the second thermal conductor 2 can be easily wound. Note that the stress relaxation structure 10 does not necessarily include the core material 4 as long as the first thermal conductor 1 and the second thermal conductor 2 can be wound.

  Further, the stress relaxation structure 10 of the present embodiment is composed of the first thermal conductor 1 and the porous metal foil, which are metal foils, on the end surface of the winding body 3 in the winding axis direction, that is, the axial direction of the core material 4. A certain second heat conductor 2 is exposed.

  Hereinafter, an example of the manufacturing method of the stress relaxation structure 10 of this embodiment is demonstrated. 3 and 4 are schematic views illustrating an example of a method for manufacturing the stress relaxation structure 10 of the present embodiment.

  In order to manufacture the stress relaxation structure 10, first, a porous metal foil that is the second heat conductor 2 is continuously formed in the winding direction on the surface of the metal foil that is the first heat conductor 1. . More specifically, for example, a copper foil is prepared as the metal foil of the first heat conductor 1, and a porous metal foil made of the above-described porous film by electroless copper plating is formed on the surface thereof. Thereby, the porous metal foil which is the second heat conductor 2 is formed on the surface of the metal foil which is the first heat conductor 1. The second thermoelectric conductor formed by this plating can absorb the strain generated between the members and relieve the thermal stress.

  Next, as shown in FIG. 3, a core material 4 is prepared, and one end in the longitudinal direction of the first heat conductor 1 to which the second heat conductor 2 is bonded is fixed to the core material 4. More specifically, for example, a copper rod is prepared as the core material 4, and the second heat conduction is performed on the copper rod by, for example, laser welding, resistance welding, low-temperature sintered metal bonding, solder bonding, or resin bonding. One end in the longitudinal direction of the first thermal conductor 1 to which the body 2 is joined is joined.

  Next, the first thermal conductor 1 and the second thermal conductor 2 fixed to the core material 4 are wound around the core material 4 as shown in FIG. And the termination | terminus part of the 2nd heat conductor 2 is fixed. More specifically, for example, the first heat conductor 1 and the second heat conductor 2 are wound around the core material 4 until the outer diameter becomes approximately 5 mm, and the sintered copper bonding material is formed at the terminal portion. The terminal portion can be fixed by applying a copper oxide paste and heating in hydrogen at 350 ° C. for 5 minutes. Moreover, you may fix the terminal part of the 1st heat conductor 1 and the 2nd heat conductor 2 after winding by laser welding, resistance welding, solder joining, resin adhesion, etc.

  Finally, the first heat conductor 1 and the second heat conductor 2 wound around the core material 4 are cut to a thickness of, for example, about 1 mm by, for example, a discharge wire, a diamond cutter, or the like. The stress relaxation structure 10 provided with the wound body 3 shown in FIGS. 1 and 2 can be obtained.

[Thermoelectric conversion module]
Next, an embodiment of the thermoelectric conversion module of the present invention will be described in detail with reference to the drawings.

  FIG. 5 is a schematic cross-sectional view of the thermoelectric conversion module 100 of the present embodiment. The thermoelectric conversion module 100 of this embodiment is characterized by including the above-described stress relaxation structure 10 and the thermoelectric conversion element 20 joined to the stress relaxation structure 10. In the thermoelectric conversion module 100 of the present embodiment, the stress relaxation structure 10 and the thermoelectric conversion element 20 are joined via the metal layer 30. As a material of the metal layer 30, for example, a low-temperature sinterable metal paste material made of copper oxide can be used. The stress relaxation structure 10 and the thermoelectric conversion element 20 may be joined by a brazing material.

  The thermoelectric conversion module 100 of this embodiment includes two types of thermoelectric conversion elements 20, that is, a P-type thermoelectric conversion element 20 </ b> P and an N-type thermoelectric conversion element 20 </ b> N. The thermoelectric conversion element 20 is an element that generates a current due to a temperature difference between the pair of end faces 20a and 20b. The P-type thermoelectric conversion element 20P is, for example, a silicon-germanium element, and flows current from the high temperature side to the low temperature side. The N-type thermoelectric conversion element 20N is, for example, a silicon-magnesium element, and allows a current to flow from the low temperature side to the high temperature side.

  The linear expansion coefficient of the silicon-germanium element that is the P-type thermoelectric conversion element 20P is, for example, about 3.5 ppm / ° C. The linear expansion coefficient of the silicon-magnesium element that is the N-type thermoelectric conversion element 20N is, for example, about 15.5 ppm / ° C.

  The thermoelectric conversion module 100 of the present embodiment further includes a wiring substrate 40 bonded to the stress relaxation structure 10 and a copper electrode 50 bonded to the thermoelectric conversion element 20.

  The wiring board 40 has, for example, a copper wiring 42 on the surface of a ceramic substrate 41 such as aluminum nitride, and stress relaxation in which the thermoelectric conversion element 20 is joined in the winding axis direction of the winding body 3 of the thermoelectric conversion module 100. The structure 10 is joined to the end surface 10b opposite to the end surface 10a. In the thermoelectric conversion module 100 of the present embodiment, the stress relaxation structure 10 and the wiring board 40 are bonded via the metal layer 30. As a material of the metal layer 30, for example, a low-temperature sinterable metal paste material made of copper oxide can be used.

  The copper electrode 50 is soldered using, for example, a sheet-like Sn-3.5Ag-1.5Cu alloy on the end surface 20b opposite to the end surface 20a of the thermoelectric conversion element 20 to which the stress relaxation structure 10 is bonded. Has been. That is, the copper electrode 50 is joined to the end face 20 b of the thermoelectric conversion element 20 via the solder layer 60. The reflow temperature in solder joint is about 270 ° C., for example.

  The thermoelectric conversion module 100 may have a sealing layer that is formed by a sealing technique using a glass material or a resin material and seals the thermoelectric conversion module 100. Examples of the resin material used for the sealing layer include epoxy resin, polyamideimide, polyimide, and silicon resin. Examples of the glass material used for the sealing layer include low melting point vanadium glass. Moreover, it is possible to improve the reliability of a junction part by forming the sealing layer which seals a junction part using vacuum sealing or an inert sealing technique.

  Hereinafter, an example of the manufacturing method of the thermoelectric conversion module 100 of this embodiment is demonstrated. 6A to 6F are schematic cross-sectional views illustrating each step of the method for manufacturing the thermoelectric conversion module 100.

  In order to manufacture the thermoelectric conversion module 100, first, as shown in FIG. 6A, a paste 30p of a low-temperature sinterable metal material is formed in an area corresponding to the installation position of the thermoelectric conversion element 20 on the copper wiring 42 of the wiring board 40. Apply. Further, the region can be coated with a low temperature sinterable metal material by plating or the like.

  The low-temperature sinterable metal material includes any of metal particles, metal oxide particles, and metal salt particles. Examples of metal particles include silver, copper, gold, platinum, palladium, rhodium, osmium, ruthenium, iridium, iron, tin, zinc, cobalt, nickel, chromium, titanium, tantalum, tungsten, indium, silicon, and aluminum. From one kind of metal or an alloy made of two or more kinds of metals can be used. As the oxide particles, gold oxide, silver oxide, silver oxide, cupric oxide can be used. As a metal salt particle, silver acetate, a neodecanoic acid silver salt, etc. can be used as a carboxylic acid metal salt.

  When the low temperature sinterable metal material contains silver or copper particles, it is preferable to use particles having an average particle size of more than 1 nm and 100 μm or less. In order to prevent the particles from aggregating, it is preferable to coat these particles with an organic dispersant. Examples of the dispersant include alkyl carboxylic acids and alkyl amines.

  When the low-temperature sinterable metal material contains silver oxide particles, it contains a reducing agent made of an organic substance and a solvent in addition to the silver oxide particles. When the low temperature sinterable metal material contains copper oxide particles, it contains a paste solvent in addition to the copper oxide particles. The average particle diameter of the metal oxide particles contained in the low temperature sinterable metal material is preferably 1 nm or more and 50 μm or less. As content of a metal oxide particle, it is preferable to set it as more than 50 mass parts and 99 mass parts or less in all the mass parts in a low-temperature-sinterable metal material. The higher the metal content in the low-temperature sinterable metal material, the fewer organic residues will be left after bonding at low temperatures, and a dense fired layer can be formed at low temperatures, and metal bonds can be formed at the bonding interface. . As a result, the bonding strength is improved, and furthermore, a metal layer having high heat dissipation and high heat resistance can be formed. However, when the metal content in the low-temperature sinterable metal material exceeds 99 parts by mass, the organic matter necessary for reduction is lost and reduction sintering cannot be performed.

  As the reducing agent made of an organic substance contained in the low-temperature sinterable metal material, for example, any of alcohols, carboxylic acids, and amines is preferable. Among these, alcohols with a small environmental load are preferable. Examples of usable alcohol-containing compounds include alkyl alcohols, such as heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, dodecyl alcohol, tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, hexa There are decyl alcohol, heptadecyl alcohol, octadecyl alcohol, nonadecyl alcohol, and icosyl alcohol. Furthermore, not only the primary alcohol type, but also alcohol compounds having secondary alcohol type, tertiary alcohol type, alkanediol, and cyclic type structures can be used. In addition, compounds having a large number of alcohol groups such as ethylene glycol and triethylene glycol may be used.

  The content of the reducing agent contained in the low-temperature sinterable metal material is preferably in the range of 1 part by mass to 50 parts by mass with respect to the total weight of the silver oxide particles. This is because if the amount of the reducing agent is less than 1 part by mass, the amount is not sufficient to reduce the metal particle precursor in the bonding material to produce metal particles. Moreover, when the quantity of a reducing agent exceeds 50 mass parts, the residue after joining will increase. As a result, metal bonding at the interface and densification in the bonding silver layer are difficult. It is also possible to mix and use metal particles having a relatively large average particle size of about 50 μm to 100 μm in the bonding material. This is because the metal particles having an average particle diameter of 100 nm or less produced during bonding play a role of sintering metal particles having an average particle diameter of about 50 μm to 100 μm. Further, metal particles having a particle size of 100 nm or less may be mixed in advance.

  When a low-temperature sinterable metal material is used as the paste 30p, a solvent may be added to the low-temperature sinterable metal material. Examples of the solvent include alcohols. It can be used as a solvent. As alcohols, heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, dodecyl alcohol, tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, hexadecyl alcohol, heptadecyl alcohol, octadecyl alcohol, nonadecyl alcohol, There is icosyl alcohol. Further, glycols such as diethylene glycol, ethylene glycol, triethylene glycol, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, and diethylene glycol diethyl ether can be used. Furthermore, not only the primary alcohol type, but also a secondary alcohol type, a tertiary alcohol type, an alkanediol, and an alcohol compound having a cyclic structure can be used. In addition, terpineol, ethylene glycol, or triethylene glycol may be used. Among these, it is preferable to use a glycol-based solvent. This is because glycol-based solvents are inexpensive and have little toxicity to human bodies. Furthermore, since these alcohol-based solvents can act not only as a solvent but also as a reducing agent for silver oxide, they can be used by adjusting to an appropriate amount as a reducing agent for the amount of silver oxide particles. it can. As the solvent for the paste, a solvent having a boiling point of 350 ° C. or lower can be used as in the case of using silver particles and copper particles. Also when a low-temperature sinterable metal material containing silver oxide particles is made into a paste, a solvent having a boiling point of 350 ° C. or lower can be used.

  Next, as illustrated in FIG. 6B, the stress relaxation structure 10 is disposed in a region on the wiring substrate 40 corresponding to the installation position of the thermoelectric conversion element 20 via the paste 30p of the low-temperature sinterable metal material.

  Next, as shown in FIG. 6C, a paste 30p of a low-temperature sinterable metal material is applied to the end face 10a opposite to the end face 10b facing the wiring board 40 of the stress relaxation structure 10.

  Next, as shown in FIG. 6D, the thermoelectric conversion element 20 is placed on the end surface 10 a opposite to the end surface 10 b facing the wiring substrate 40 of the stress relaxation structure 10 via a paste 30 p of a low-temperature sinterable metal material. Deploy. Then, for example, the substrate is heated to about 350 ° C. in a hydrogen atmosphere, and the wiring board 40, the stress relaxation structure 10, and the thermoelectric conversion element 20 are pressurized at a pressure of 1.0 MPa in the stacking direction. Thereby, the paste 30p of the low-temperature sinterable metal material is sintered, and as shown in FIG. 6E, the wiring board 40 and the stress relaxation structure 10 are joined via the metal layer 30, and the stress relaxation structure 10 and The thermoelectric conversion element 20 is joined via the metal layer 30.

  In addition, the atmosphere at the time of sintering the paste 30p of the low-temperature sinterable metal material is any of the atmosphere, nitrogen, and reducing atmosphere when the low-temperature sinterable metal material includes silver particles and silver oxide particles. Can also be implemented. On the other hand, when the low-temperature sinterable metal material contains copper particles and copper oxide particles, it is necessary to sinter the low-temperature sinterable metal material in a reducing atmosphere such as hydrogen or formic acid. This is because it is necessary to use a reducing atmosphere in order to reduce and bond the copper particles and the copper oxide particles.

  Moreover, the pressure which pressurizes the wiring board 40, the stress relaxation structure 10, and the thermoelectric conversion element 20 in these lamination directions at the time of sintering of the paste 30p of a low temperature sintering metal material shall be larger than 0 MPa and 30 MPa or less. Can do. By applying pressure, the metal layer 30 can be densified and the reliability of the bonding layer can be improved. However, if the pressure exceeds 30 MPa, the thermoelectric conversion element 20 may be damaged. The sintering time can be longer than 1 second and shorter than 180 minutes.

  Finally, as shown in FIG. 6F, for example, using a sheet-like Sn-3.5Ag-1.5Cu alloy 60m, the opposite side to the end face 20a of the thermoelectric conversion element 20 to which the stress relaxation structure 10 is bonded. The copper electrode 50 is soldered to the end face 20b. Thereby, the copper electrode 50 is joined to the end surface 20 b of the thermoelectric conversion element 20 via the solder layer 60. The reflow temperature in solder joint is about 270 ° C., for example. As described above, the thermoelectric conversion module 100 shown in FIG. 5 can be manufactured.

  Hereinafter, the operation of the stress relaxation structure 10 of the present embodiment and the thermoelectric conversion module 100 using the same will be described.

  The thermoelectric conversion module 100 of the present embodiment is used, for example, with the wiring board 40 side as a high temperature side and the copper electrode 50 side as a low temperature side. More specifically, for example, the wiring board 40 is attached to a high-temperature body that is a heat source such as an exhaust pipe of an automobile so that heat can be transferred, and the copper electrode 50 side is cooled by air cooling or water cooling.

  Thereby, in the thermoelectric conversion module 100, the temperature of the high-temperature side wiring board 40 rises to, for example, about 500 ° C., and the cooled copper electrode 50 becomes the low-temperature side, and the thermoelectric conversion element 20 and the wiring board 40 side. A temperature difference occurs on the copper electrode 50 side. Due to this temperature difference, the P-type thermoelectric conversion element 20P causes a current to flow from the high temperature side to the low temperature side, and the N type thermoelectric conversion element 20N causes a current to flow from the low temperature side to the high temperature side, thereby generating an electromotive force. Can generate electricity.

  However, the linear expansion coefficient of the silicon-germanium element that is the P-type thermoelectric conversion element 20P is different from the linear expansion coefficient of the silicon-magnesium element that is the N-type thermoelectric conversion element 20N. Therefore, when the stress relaxation structure 10 is not provided, heat is generated between the thermoelectric conversion element 20 and the wiring substrate 40 due to a heat cycle during power generation of the thermoelectric conversion element 100 or heat during manufacture of the thermoelectric conversion element 100. There is a possibility that the stress due to the difference in expansion amount acts and distortion occurs, the joint between the thermoelectric conversion element 20 and the wiring board 40 is broken, or the thermoelectric conversion element 20 is damaged.

  In contrast, the thermoelectric conversion module 100 of the present embodiment includes the stress relaxation structure 10 and the thermoelectric conversion element 20 joined to the stress relaxation structure 10. In addition, the stress relaxation structure 10 of the present embodiment includes a wound body 3 in which the first thermal conductor 1 and the second thermal conductor 2 are alternately wound, and the first thermal conductor 1 Is a metal foil, and the second heat conductor 2 is a porous metal foil.

  Therefore, the heat on the high temperature side can be efficiently transferred to the thermoelectric conversion element 20 by the metal foil and the porous metal foil having high thermal conductivity of the wound body 3 constituting the stress relaxation structure 10. Further, the wound body 3 of the stress relaxation structure 10 allows thermal expansion of the thermoelectric conversion element 20 by a porous metal foil that is easily deformed as compared with the metal foil, and the thermoelectric conversion element 20 and the wiring board 40 on the high temperature side. Thermal stress acting between the two can be relaxed.

  Moreover, since the 2nd heat conductor 2 is porous metal foil, compared with a carbon-type sheet material, for example, the adhesiveness with respect to the wiring board 40 or the thermoelectric conversion element 20 is favorable, and the stress relaxation structure 10 The bonding reliability between the wound body 3 and the wiring board 40 and the thermoelectric conversion element 20 is improved. Therefore, the vibration resistance of the thermoelectric conversion module 100 can be improved by using the stress relaxation structure 10 of the present embodiment.

  Further, the stress relaxation structure 10 of the present embodiment is composed of the first thermal conductor 1 and the porous metal foil, which are metal foils, on the end surface of the winding body 3 in the winding axis direction, that is, the axial direction of the core material 4. A certain second heat conductor 2 is exposed. Therefore, it is possible to easily and reliably bond the stress relaxation structure 10 to the wiring board 40 and the thermoelectric conversion element 20 and improve the bonding reliability.

  Further, in the stress relaxation structure 10 of the present embodiment, the material of the metal foil that is the first thermal conductor 1 and the porous metal foil that is the second thermal conductor 2 constituting the wound body 3 is copper or In the case of nickel, the thermal conductivity and bonding reliability of the stress relaxation structure 10 can be further improved.

  Further, in the stress relaxation structure 10 of the present embodiment, the wound body 3 includes the core material 4, and the first heat conductor 1 and the second heat conductor 2 are integrated around the core material 4. It is wound around. Thereby, winding of the winding body 3 can be made easy and manufacture of the stress relaxation structure 10 can be made easy. Moreover, when the core material 4 has a plate shape, the wound body 3 having a substantially rectangular end surface can be manufactured. By making the core material 4 into a plate shape, the wound body 3 also has a plate shape. Since the element on which the stress relaxation structure 10 is installed is also plate-shaped, useless areas can be reduced, and the packing density of the element is improved.

  Moreover, in the thermoelectric conversion module 100 of this embodiment, the stress relaxation structure 10 and the thermoelectric conversion element 20 are joined via the metal layer 30. Since the metal layer 30 has high heat resistance, it is possible to improve the bonding reliability between the wiring board 40 on the high temperature side near the heat source and the thermoelectric conversion element 20. Further, the metal layer 30 is strong against the metal foil that is the first heat conductor 1 and the porous metal foil that is the second heat conductor 2 constituting the wound body 3 of the stress relaxation structure 10. Bonded and the stress relaxation structure 10 can be firmly bonded to the wiring substrate 40 and the thermoelectric conversion element 20. Therefore, the bonding reliability between the stress relaxation structure 10, the wiring substrate 40 and the thermoelectric conversion element 20 can be improved, and the vibration resistance of the thermoelectric conversion module 100 can be improved.

  As described above, according to this embodiment of the present invention, the stress relaxation structure 10 that can achieve both thermal conductivity and thermal stress relaxation and has excellent vibration resistance, and the stress relaxation structure 10. The thermoelectric conversion module 100 provided with can be provided.

[Insulated substrate]
The stress relaxation structure 10 of this embodiment can also be used for an insulating substrate for a thermoelectric conversion module. FIG. 7 is a schematic cross-sectional view of an insulating substrate 200 using the stress relaxation structure 10 of the present embodiment. The insulating substrate 200 includes a ceramic substrate 70 whose surface is plated with Ni, a stress relaxation structure 10 bonded to the surface of the ceramic substrate 70 via a metal layer 30, and a stress relaxation structure 10 via the metal layer 30. Bonded copper wiring 80 is provided.

  The ceramic substrate 70 is a square silicon nitride thin plate having a thickness of 0.6 mm, a length of 100 mm, and a width of 100 mm, for example, and the thickness of the copper wiring 80 is, for example, 0.4 mm. The metal layer 30 is, for example, a copper paste in which copper particles having an average particle diameter of 1 μm are dispersed in triethylene glycol as a low-temperature sinterable metal material, applied to a portion where the metal layer 30 is formed, and in a hydrogen atmosphere Can be formed by heating to 400 ° C. and baking for 15 minutes. You may cut | disconnect the excess part of an outer peripheral part with a discharge wire after baking of the metal layer 30. FIG.

  Since the insulating substrate 200 shown in FIG. 7 is used in a portion close to the heat source, high reliability is required even at a high temperature. However, by providing the stress relaxation structure 10 described above, the thermal conductivity and thermal stress relaxation properties can be achieved. The insulating substrate 200 can be compatible and has excellent vibration resistance and high reliability. Such an insulating substrate 200 can be suitably used in a field such as a power module where the use temperature is increasing.

  The embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  Hereinafter, a stress relaxation structure according to an example of the present invention and a stress relaxation structure according to a comparative example as a comparison target will be described.

[Example]
As a metal foil of the first heat conductor, a copper foil (product number: CU-113213) manufactured by Niraco Co., Ltd. having a thickness of 0.020 mm, a width of 100 mm, and a length of 300 mm was prepared. Next, a 5 μm-thick porous film is formed on the surface of the prepared copper foil by electroless copper plating described in Journal of Japan Institute of Electronics Packaging, Vol. 1 (1998), No. 1, P66-69. Then, the porous metal foil which is the second heat conductor was joined to the metal foil of the first heat conductor.

  Next, a cylindrical copper rod having a diameter of 2.0 mm (product number: CU-112544) manufactured by Niraco Co., Ltd. is prepared as a core material, and the first thermal conductor and the first core are prepared by laser welding on the prepared core material. One end in the longitudinal direction of the heat conductor 2 was fixed. Then, the first heat conductor and the second heat conductor are wound around the core material, and a copper oxide paste, which is a low-temperature sintered metal material, is applied to the end portion in the longitudinal direction, and is placed in a hydrogen atmosphere for 5 minutes. Then, it was heated to 350 ° C. to fix the end portion in the longitudinal direction. The outer diameters of the wound first heat conductor and second heat conductor were about 5 mm.

  Finally, the first thermal conductor and the second thermal conductor wound around the core are cut with a discharge wire to form a wound body having a thickness of about 1 mm, and the stress relaxation structure of the example Got. The obtained stress relaxation structure includes a wound body in which the first heat conductor and the second heat conductor are alternately wound, and the first heat conductor is a metal foil, The heat conductor was a porous metal foil. Further, the first heat conductor and the second heat conductor were joined to each other.

  Next, a joint strength test of the stress relaxation structure was performed. First, two disk-shaped copper plates having a diameter of 10 mm and a thickness of 5 mm were prepared. And the copper oxide paste which is a low-temperature sintering metal material was apply | coated to the one end surface of the winding axis direction of the winding body of a stress relaxation structure body, and the other end surface, respectively, and the prepared copper plate was arrange | positioned 1 sheet at a time. Then, under a hydrogen atmosphere, a pressure of 1.0 MPa is applied in the stacking direction of the copper plate and the stress relaxation structure and heated to 350 ° C. for 5 minutes. One of the windings of the stress relaxation structure in the winding axis direction A copper plate was joined to each of the end face and the other end face through a metal layer to obtain a test piece.

  Next, a shear stress of 30 mm / min was applied to the obtained test piece using a bond tester SS-100KP with a maximum load of 100 kg manufactured by Seishin Shoji Co., Ltd., and the maximum load at break was measured. Then, the bonding strength was obtained by dividing the measured maximum load by the bonding area.

[Comparative example]
Except for using a carbon sheet as the second thermal conductor constituting the wound body and laminating the first thermal conductor and the second thermal conductor without bonding, the stress relaxation structure of the above-described embodiment The stress relaxation structure of the comparative example was manufactured similarly to the body. A carbon sheet having a thickness of 0.020 mm, a width of 100 mm, and a length of 300 mm was used. And like the stress relaxation structure of an Example, the test piece was manufactured, the maximum load at the time of a fracture | rupture was measured with the shear test machine, and the joint strength was calculated | required by dividing the measured maximum load by a joining area.

  FIG. 8 shows the relationship between the initial bonding strength of the stress relaxation structure of the example and the initial bonding strength of the stress relaxation structure of the comparative example. As shown in FIG. 8, when the initial joint strength of the stress relaxation structure of the comparative example was 1, the initial joint strength of the stress relaxation structure of the example increased to 1.2 or more. Here, the initial bonding strength of the stress relaxation structure of the comparative example was 10 MPa, and the initial bonding strength of the stress relaxation structure of the example was 12 MPa.

  The wound body of the stress relaxation structure used for the test piece of the example uses a porous metal foil as the second heat conductor. Therefore, on the end surface in the winding axis direction of the wound body, not only the portion where the metal foil as the first thermal conductor is exposed, but also the portion where the porous metal foil is exposed is joined to the copper plate by the metal layer, Bonding strength was improved.

  On the other hand, the wound body of the stress relaxation structure used for the test piece of the comparative example uses a carbon sheet as the second heat conductor. Therefore, on the end surface in the winding axis direction of the wound body, the portion where the carbon sheet is exposed is not bonded to the copper plate by the metal layer, and the bonding strength is reduced.

  From the above, it was confirmed that the stress relaxation structure according to the example of the present invention was superior in bondability to a metal member and superior in vibration resistance than the stress relaxation structure according to the comparative example.

DESCRIPTION OF SYMBOLS 1 1st heat conductor 2 2nd heat conductor 3 Winding body 4 Core material 10 Stress relaxation structure 20 Thermoelectric conversion element 30 Metal layer 100 Thermoelectric conversion module.

Claims (9)

A stress relaxation structure comprising a wound body in which a first heat conductor and a second heat conductor are alternately wound,
The stress relaxation structure, wherein the first thermal conductor is a metal foil, and the second thermal conductor is a porous metal foil.   The stress relief structure according to claim 1, wherein the metal foil and the porous metal foil are made of copper or nickel.   The wound body includes a core material, and the first heat conductor and the second heat conductor are alternately wound around the core material. The stress relaxation structure according to claim 2.   The stress relaxation structure according to claim 3, wherein the core member has a plate shape.   The stress relaxation structure according to claim 1, wherein the first thermal conductor and the second thermal conductor are joined.   2. The stress relaxation structure according to claim 1, wherein both the metal foil and the porous metal foil are exposed at an end surface in a winding axis direction of the wound body. Said second thermal conductor, the stress relaxation structure according to claim 1, characterized in that said a first heat transfer conductive porous coating formed on the surface of the.   A thermoelectric conversion module comprising: the stress relaxation structure according to any one of claims 1 to 7; and a thermoelectric conversion element bonded to the stress relaxation structure.   The thermoelectric conversion module according to claim 8, wherein the stress relaxation structure and the thermoelectric conversion element are bonded via a metal layer.

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